The invention relates to a process and apparatus for microbiological degradation of organic wastes, which are introduced batchwise into a vessel closed on all sides for the purpose of forced discontinuous aeration and, after the microbiological degradation has taken place, are mechanically discharged from the vessel.
It also relates to a process for separating organic impurities from waste gases which are forced through a biomass, surrounded by a vessel, as absorbent, wherein the impurities are at least partially degraded by metabolic processes of microorganisms colonizing the absorbent.
In the so-called Blaubeuer aeration process, the heap of organic wastes, which is to be microbiologically degraded and is preferably arranged on a perforated plate, is aerated by sucking through or blowing in air from below in surges interrupted by pauses, the pauses being of such a length that the temperature in all layers of the heap is the same and the oxygen content in the waste air does not fall below 10% by volume.
Even though it showed excellent rotting results, this discontinuous process has been replaced by continuously operating large-scale rotting processes, in which the rotting material passes continuously from top to bottom through an aeration reactor and the entire atmospheric oxygen required for the rotting process is introduced from the bottom of the aeration reactor into the latter, likewise continuously, in a counter-current process in such a way that, in the aeration reactor, different temperature and O.sub.2 zones are formed, of which the zone of highest temperature is located in the upper third and the zone of lowest temperature is located in the outlet, and the zone of highest oxygen content is located at the bottom and the zone of lowest oxygen content is located in the uppermost layer within the heap in the aeration reactor. Reference is made to British Patent Specification 1,402,955.
In place of a purely aerobic microbiological degradation of the organic wastes, anaerobic microorganisms also participate in the degradation of the wastes in the last mentioned, continuously operating process, so that an optimization of the technical imitation of the natural degradation conditions occurring in nature is obtained, since in each case all microorganisms participating in the natural microbiological degradation of organic wastes are employed on a large scale.
Such a continuously operating process, however, presupposes a reliably functioning technology, which so far has not been possible to be realized in spite of many efforts. This becomes particularly critical for large units, where rotting vessels of a capacity of more than 1200 m.sup.3 are used. Even the introduction of the wastes causes difficulty, for example in the case of introduction via spinning plates, a selection of the organic wastes by gravity takes place, leading to different density conditions within the heap. Uniform aeration and hence uniform microbiological degradation can, however, be achieved only if a heap of identical density can be subjected uniformly to forced aeration over the cross-section, that is to say the same resistance over the entire cross-section; as is known, the air which is injected or extracted seeks out the route of least resistance through the heap. Similar comments apply to the discharge which must likewise take place uniformly over the entire cross-section of the heap. Irregularities in the mechanical feed and discharge thus lead to different air resistances, so that so-called air bridges result which in turn cause different temperature zones, drying-out and/or wetting of individual regions of the heap which is to be aerated in a predetermined manner. In addition, compaction zones are formed which, although they migrate in some cases through the vessel, cause considerable disturbances on discharge at the latest. As soon as the continuous operation is disturbed, the entire biology gets out of control, so that the total vessel must be emptied, which frequently leads to intolerable technical difficulties. The operating personnel also has to meet stringent requirements with respect to knowledge of the particular causes of the disturbances arising and of possibilities of overcoming them.
As is known, the collected domestic trash or garbage varies widely from day to day in its structure, with high organic contents which, as a rule, are very moist. Very frequently, the trash has a high content of paper and cardboard, quite apart from so-called ballast materials such as plastic bags and the like, which cause hard, air-impermeable layers in the vessel. The density differences due to the gravity selections during charging also leads to different air resistances, which inevitably cause irregular degradation results and hence also irregular discharge results. The entire biological degradation is thus pushed out of equilibrium. Increased air feed then leads to so-called snuffing of the biology within the heap in the vessel, and this causes caking of the heap and hence a rock-hard conglomerate--similar to "nadelflur"--which cannot be discharged either by means of chain cutters or worm-wheel cutting machines. "Nadelflur" is a conglomerate of fir needles which may form the ground of a forest and represents a layer permeable to air.
It is also known to subdivide the entire heap, which is to be continuously degraded and is located in a vessel, by means of grids and cutting tools associated with these grids into individual sections of different sizes, in order to facilitate the transport of the individual particles of the heap through the vessel. Reference is made to U.S. Pat. No. 2,680,069.
Such a subdivision of the transport of the particles of the heap leads, however, to extremely poor microbiological degradation results, since there is great interference with the activity of the microorganisms due to the multiple mechanical intervention and, in particular, the mycelium threads which are formed are torn again and again. In addition, new air bridges are continuously created, so that the air fed can escape in an uncontrolled fashion without having been able to be utilized for breathing by the microorganisms becoming active.